Thermoplastic polymers find use in a variety of plastic articles including, but not limited to films, sheets, adhesives, binders, laminates, coatings, fibers, foams, molded articles, and the like. Often, the plastic articles have a short use cycle, as in the areas of packaging, agriculture, household goods, and personal care products. For example, in the packaging of food, plastic articles often play the role of a protective agent and are quickly disposed of after the food is consumed. Likewise, plastic household articles such as detergent bottles, and plastic personal care products such as diapers and tampon applicators, are discarded upon use.
Typically, plastic articles are made from petroleum-based thermoplastic polymers including, but not limited to, polyolefins. However, the use of petroleum-based thermoplastic polymers is becoming less pragmatic due to disruptions in petroleum supply and increasing expense. Additionally, after use it is common for petroleum-based plastic materials, which are typically not biodegradable, to become solid waste that is to be discarded in rapidly vanishing, increasingly expensive landfill space.
Thermoplastic starch (TPS) has been identified as a substitute for petroleum-based polymers. The use of TPS is advantageous since starch is naturally abundant, and relatively inexpensive. Moreover, TPS has desirable properties not typically observed in conventional petroleum-based polymers including, but not limited to, biodegradability, natural hydrophilicity and compatibility with materials traditionally incompatible with petroleum-based polymers.
To render starch thermoplastic for processing, it is typically combined with one or more plasticizers and/or other processing aids. Like many petroleum-based polymers, TPS may be processed using conventional means including, but not limited to, melt spinning and other melt extrusion techniques. However, unlike many petroleum-based polymers, TPS is susceptible to moisture. When exposed to water, TPS can partially or even fully disintegrate within hours. This susceptibility to moisture can limit the applications in which TPS may be utilized. One proposed solution to overcome the susceptibility of TPS to water is to blend it with petroleum-based polymers including, but not limited to, polyolefins. However, the addition of petroleum-based polymers to TPS may propagate disadvantages such as those described above.
There remains a need for water stable thermoplastic polymer compositions made from abundant, low-cost starch. The thermoplastic polymer compositions would advantageously be water stable without requiring the use of additives including, but not limited to, petroleum products and the like.
A further need remains for water stable plastic articles comprising TPS compositions, which may optionally be biodegradable. It would also be advantageous for such articles to be water stable without requiring the use of additives including, but not limited to, petroleum based products and the like.
It is also desirable to provide starch compositions that may be converted into water stable thermoplastic polymer compositions. Plastic articles made from such compositions could be rendered water stable during or after processing. Additionally, it is desirable to provide the starch compositions, and/or components thereof, in forms that are easy to make, ship, process, and combinations thereof.